Running without food may result in low blood sugar. Normally food is converted to glucose by the digestive system into the bloodstream, which is transported to cells throughout the body as a source of energy. Glycogen that is not consumed is converted to glycogen and stored in the liver and muscles. If too much sugar is consumed, the excess is converted to fat. A blood sugar concentration below 2.8 mmol/L is called hypoglycemia. Some groups of people who are thin, chronically hungry, or suffering from underlying diseases will experience hypoglycemia when running on an empty stomach because of the accelerated decomposition of hepatic glycogen as well as muscle glycogen due to the excessive consumption of energy by exercise. Normal people occasionally run without eating, generally the probability of hypoglycemia is lower. However, running will consume a lot of energy, and prolonged running may cause hypoglycemic reaction. It is recommended to eat appropriate carbohydrate food, such as bread and sweet potato, before running to avoid hypoglycemia.